The present invention relates to a centrally-activated deferred action battery constituted by a stack of primary couples and in particular it relates to an arrangement for improving the electrical isolation of the couples from each other and from the central portion to prevent or minimize leakage current as the electrolyte flows to the couples during activation.
Deferred action batteries are described in French Pat. No. 1,558,423 for example. In that patent each couple comprises a negative electrode constituted by a layer of zinc, a positive electrode of silver oxide, a paper separator provided with small insulating spacer elements which delimit a gap for receiving the electrolyte, and a copper sheet separating each couple from the adjacent couple. The positive electrode of one couple and the negative electrode of the adjacent couple may both be mounted respectively on opposite sides on this copper sheet to constitute a duplex electrode. The electrodes and the copper sheet are each in the form of a disc having a hole at its center so that the stack delimits a central well through which the electrolyte is supplied to the electrodes during activation. An insulating washer is provided around the central hole of each copper disc on which a layer of zinc is mounted. These washers are intended to prevent or minimize electrical leakage currents between the couples due to the presence of a film of electrolyte on the edge of the copper disc.
However, it has been observed that during activation these washers are not able to prevent the electrical leakage currents which pass through the electrolyte while it is flowing into the couples.
Preferred embodiments of the present invention have for an object the prevention or reduction of these leakage currents without excessively hindering the flow of the electrolyte during battery activation.
The present invention provides a centrally activated battery comprising a stack of couples each constituted by a positive plate and a negative plate each having a central hole and separated from each other by a gap for receiving the electrolyte, each couple being mechanically separated from the adjacent couple and being electrically connected thereto by a metal sheet also having a central hole, each of the said sheets having a first insulating washer at its center, the hole in the center of the washer being of smaller diameter than the hole in the center of the sheet, and cooperating with a second insulating washer to insulate the inner edge of the said sheet, wherein one face of the first washer rests on the second washer of the adjacent sheet and includes at least one recess such that the recess together with the said second washer of the adjacent sheet forms a channel for conveying electrolyte from the central space or well to the said gap and wherein the recess is so shaped that the channel follows a path which is oblique to the local radial direction of the central hole.
The channel is preferably curved.
In this way the electrolyte flows into the electrolyte-receiving gap of each couple via channels which are of restricted cross-section and whose oblique and curved paths are longer than a directly radial path, thereby considerably increasing the electrical resistance to leakage currents during activation of the battery.
Preferably the curvature of the channels is towards the center of the hole in order to facilitate the flow of electrolyte towards the couples. Advantageously the channels widen out towards the outer edge of the washers to better distribute the electrolyte.